For a plurality of applications, fluids, in particular liquids, are conducted through a microfluid system for a prolonged period of time. Possible applications in this respect are e.g. biofilm examinations or the monitoring of cells under continuous flow conditions. Such examinations are used e.g. in the field of atherosclerosis research or in connection with adhesion phenomena (e.g. rolling).
In the case of conventional systems with an open circuit, a liquid to be transported or conveyed is provided in a separate reservoir, e.g. a beaker. With the aid of a pump, e.g. a diaphragm pump or a peristaltic pump, this liquid is conducted from the reservoir through a flow chamber, e.g. in the form of a channel.
The amount of liquid available for flow-though in such systems is limited especially by the dimensions of the reservoir. Typical liquid volumes lie between 1 ml and 500 ml.
The amount of liquid used depends, inter alia, on the respective costs, e.g. the price of the dissolved agents, and the requirements that have to be met with regard to a physiologically relevant geometry and dimensioning of the flow chamber. The ratio of flow chamber width to flow chamber height that is typically chosen is a ratio between 5:1 and 100:1. The flow rates are determined by the channel dimensions and also by experimental questioning. Microfluid channels have, typically, a volume of 0.1 μl to 1000 μl; typical flow rates range from 0.5 ml/min to 500 ml/min.
In the case of the above-mentioned fluid volumes in the reservoir, the whole reservoir volume is consequently conducted through the microfluid system within a period of 2 minutes to approx. 16 hours. The liquid conducted through the microfluid system is then also received by and accommodated in a separate reservoir. When this liquid is conveyed through the microfluid system once more, this will be done in the opposite the direction of flow.
Alternatively to open circuits also closed circuits can be used, in the case of which a single separate liquid reservoir is provided, from which the liquid is taken and into which the liquid is returned after having flown through the flow chamber.
In the case of closed circuits, peristaltic pumps are normally used. However, this pump mechanism leads to an intensive mechanical load e.g. on cells suspended in the liquid. Hence, effects to be examined will be influenced in an undesirable way; this may e.g. lead to an unspecific activation of immune cells whose adhesion characteristics should, however, be examined on the basis of specific activation.